He said he saw several attackers taunt a rival gang member who was badly injured.

“I just saw three dead on the sidewalk outside of my unit. One guy is still alive and breathing, but just barely,” the inmate said.

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The riot was the latest violence in the South Carolina prisons system, where at least 13 other inmates have been killed by fellow prisoners since the start of 2017.

It was the most inmates killed in a single riot in the US since nine prisoners and a guard died in 1993 at Southern Ohio Correctional Facility, said Steve Martin, a consultant who helps the federal government monitor prison systems.

Hours after the violence started, no correctional officers or medical personnel had attended to the dead or dying, he said.

“The COs (corrections officers) never even attempted to render aid, nor quell the disturbance,” he said. “They just sat in the control bubble, called the issue in, then sat on their collective asses.”

Mr Stirling said the response teams entered as fast as they could.

“We gathered as many people as we could, as quickly as we could and went in as soon as we thought it was safe for our staff,” he said.

The inmate told AP he knew at least two of the dead men well. He said he saw an inmate trying to get up before he “started into that ‘death rattle’ people often hear about, but never experience first hand”.

Most of the killed inmates were stabbed with homemade knives or slashed, while the remainder appeared to have been beaten, Lee County coroner Larry Logan said.

Mr Stirling said an investigation would determine if any other type of weapon was used.

The dead men were serving between 10 years and life and their crimes ranged from murder to burglary to trafficking crack cocaine. They youngest was 28 while the oldest was 44.

The injured inmates required medical attention outside the prison, which made it more difficult for authorities to restore order, Mr Stirling said.

The coroner said when he arrived it was a chaotic scene of fighting everywhere.

Mr Logan said the state-run Lee Correctional Institution, like most other South Carolina prisons, is struggling to find enough workers, but he does not believe anything could have been done once things got that far out of control.

“If everybody has an uprising, you are always going to be understaffed,” Mr Logan said.

The maximum-security facility in Bishopville houses about 1,500 inmates and there were 44 guards there when the first fight started.

Two officers were stabbed there in 2015. More recently, an inmate held a guard hostage for 90 minutes in March and another killed a fellow prisoner in February.